The storage capacity of a data storage device typified by a semiconductor memory in an information device such as a computer, a PDA (Personal Data Assistance, Personal Digital Assistants: Personal Portable Type Information Communication Device), a household game device, a digital camera, or a cellular phone, or a PHS (Personal Hand-phone System) keeps on increasing year by year. The flash memory in particular, which is a ROM (Read Only Memory) that can perform electrical erasure of and electrical writing to storage, is a nonvolatile memory from which the storage does not vanish even if external power is not supplied thereto, and is used a lot in various fields.
The flash memory also has a characteristic in which all data are collectively erased or erasure is performed block by block which is a unit of data erasure, and data writing or data reading is performed on a block-by-block basis (refer to Patent Documents 1 and 2).
The mounted capacity of the flash memory has hitherto been smaller than that of other storage device due to constraints in view of its manufacture and price. However, due to the emergence of a large capacity type memory resulting from development of a NAND-type flash memory enabling manufacture of a comparatively cheap and large-capacity memory and an NOR-type flash memory of a multi-value logical type, and an increase in the demand of a large capacity nonvolatile memory due to the spread of digital cameras and higher functions of cellar phones, the storage capacity of the nonvolatile-type semiconductor memory has been remarkably increased.
However, in many cases, due to its configuration, the NAND-type memory is based on the premise that a certain defective region may be included therein at the time of shipment to a manufacturer. Further, the NAND-type memory is often based on the premise that defects may be generated with a certain probability or in a certain amount after shipped to the manufacturer. Further, the reliability of the NOR-type flash memory, which has hitherto had higher reliability than that of other storage device, in terms of data storage, is more reduced than before because of multivaluing or the like.
[Patent Document 1]
JP Patent Kokai Publication No. JP-P2000-173289A
[Patent Document 2]
JP Patent Kokai Publication No. JP-P2002-288034A